Probing molecular motion by double-quantum (13C,13C) solid-state NMR spectroscopy: Application to ubiquitin

We demonstrate the use of two-dimensional (13C,13C) double-quantum spectroscopy to detect molecular dynamics by solid-state NMR. Data collected on tyrosine-ethylester (TEE) are in line with previously determined (1H,13C) order parameters. Application of these experiments to microcrystalline ubiquitin reveals the presence of dynamics on millisecond or faster time scales and differences in local mobility depending on microcrystal preparation. In addition, solid-state NMR-based structure calculation indicates conformational variability of loop regions between different solid-phase ubiquitin preparations. Our data relate preparation-dependent changes observed in NMR spectral parameters such as chemical shifts and through-space correlations to differences in ubiquitin dynamics and conformation and suggest a prominent role of molecular mobility in microcrystalline ubiquitin.